1. Field of the Invention
The present invention relates to a system for uniformly illuminating a liquid crystal display board from the rear side wherein a parallel light beam is emitted in the form of reflected light from a main body located behind the liquid crystal display board with substantially uniform brightness over the whole surface of the screen of the liquid crystal display board.
2. Description of the Prior Art
In recent years, a number of liquid crystal display boards have been increasingly used for word processors, personal computors and so forth to display characters, numerals or the like with a high degree of resolution. To practically activate the liquid crystal display board, a plurality of large scale integrated circuits are incorporated in a work station for each word processor or personal computor.
With the conventional liquid crystal display board practically used in that way, it has been found that the liquid crystal display board has the following drawbacks.
Although the liquid crystal display board has a high degree of resolution, it is not easy to allow brightness to be substantially uniformly distributed over the whole surface of the liquid crystal display board. In practice, brightness decreases more and more in inverse proportion to a square of the distance as measured from a light source with the result that characters, numerals or the like on the 0 screen of the liquid crystal display board are not uniformly visually recognized by an operator who is sitting in front of the word processor, personal computor or the like.
To assure that characters, numerals or the like on the screen of the liquid crystal display board are more clearly recognized by the operator, a proposal has been made such that light generated by a lamp is reflected at a reflective mirror which is disposed behind the liquid crystal display board and of which surface is treated to a frosted plane so that a parallel light beam is emitted toward the liquid crystal display board from the reflective mirror. With this proposal, however, brightness is not satisfactorily uniformly distributed over the whole surface of the liquid crystal display board. In addition, it is not easy to provide a high degree of brightness for the screen of the liquid crystal display board with the aforementioned proposal. Moreover, arrangement of the reflective mirror has been accomplished at expensive cost.